in trees during spring is supported by remobilization of stored N, so they do not depend wholly on N supplied by current-year root uptake ( Millard, 1996 ). Zavalloni (2004) found that sweet cherries absorbed little soil N before budbreak, even up
Premature defoliation of peach and nectarine (Prunus persica L. Batsch) trees resulting from foliar applications of ZnSO4 reduced N remobilization that typically occurs during leaf senescence. Leaf N remobilization in unsprayed control trees ranged from 45% to 50%, irrespective of tree N status. Leaf N remobilization in trees receiving foliar applications of ZnSO4 ranged from a positive influx of N into the leaf to ≈30% of the N remobilized, depending on ZnSO4 application timing and method of expressing leaf N levels. Early ZnSO4 applications resulted in less N remobilization. Measuring leaf N on an area basis was a more precise indicator of N remobilization than N per unit dry weight, because leaf weight per unit area changes during leaf senescence.
Soluble sugar and starch levels were measured in leaf, stem, and petiole tissues of 3 tomato (Lycopersicon esculentum Mill.) cultivars throughout plant development in order to 1) assess the contribution of reserve carbohydrates to final fruit yield and quality and 2) determine whether genotypic variation exists for this trait. In all 3 cultivars — ‘VF145B-7879’ (‘7879’), ‘UC82’ (‘82’), and ‘BL6807’ (‘6807’) — leaf tissue was found to accumulate high levels of both soluble sugars and starch. Stem and petiole tissues, although having high sugar content, accumulated little starch. An estimate of the proportion of fruit dry weight attributable to remobilization of nonstructural carbohydrate (NSC) from vine tissue was made by determining the dry weight of sugars and starch lost from vegetative tissue once the vine had ceased gaining weight and dividing by the final fruit dry weight. Values for ‘6807’ and ‘7879’ were 4.8% and 0.3%, respectively. No remobilization of NSC was apparent in ‘82’. The primary remobilized carbohydrate was leaf starch in both ‘6807’ and ‘7879’. Leaf and stem sugars were also remobilized in ‘6807’. The relatively high degree of remobilization in ‘6807’ was associated with early maturity and a high fruit/leaf ratio.
Remobilization of reserve N and uptake of soil N in winter and spring were assessed in relation to the N status of trees. Ten-year-old `Newtown Pippin' apple trees on M.7A rootstock were fertilized to create moderately vigorous trees, trees with above-ground portions (tops) and roots relatively low in N (L/L), tops high in N and roots low in N (H/L), both tops and roots high in N (H/H), or tops low in N and roots high in N (L/H). Labeled (15N) fertilizers were used to tag the soil and frame and root N pools in the moderately vigorous trees prior to winter and spring remobilization. The level of 15N in the buds and new growth was monitored throughout winter and spring. Nitrogen stored in the aerial part of the tree was first to be remobilized to meet N requirements of the developing buds. Root and soil N reached the flower buds simultaneously. Trees of the L/H treatment transported labeled N upward to the bud as early as 9 Feb., even though average air temperature was close to 7°C, whereas L/L trees did not send any root-15N to the buds until 2.5 later. When trees received an abundance of N in the fall (H/H and L/H), their buds grew faster in the spring and they bloomed earlier compared with L/L and H/L trees. For root to shoot N translocation to start early (in winter), the bud needed to be low in N and the roots had to have adequate N reserves.
Uptake, recycling, and partitioning of N in relation to N supply and dry matter partitioning was determined for 3- and 4-year-old `Elstar' apple trees [(Malus sylvestris (L) Mill. var. domestica (Borkh.) Mansf.] on Malling 9 rootstock in 1994 (year 3) and 1995 (year 4), respectively. Trees received N yearly as Ca(NO3)2 at 20 g/tree applied on a daily basis through a drip irrigation system. The fertilizer was labelled with 15N in year 3 to allow quantification of remobilization and uptake. The trees were not allowed to crop in years 1 and 2 and were not thinned in years 3 and 4, thereby establishing a range of crop loads. Dry matter and N contents were measured in fruit, midseason and senescent leaves and prunings collected in year 3, in midseason leaves, and in components of the whole trees, harvested in fall of year 4. Labelled N withdrawn from leaves in year 3 was less than that remobilized into leaves and fruit in year 4, indicating that senescent leaves were not the only source of remobilized N. Nitrogen uptake efficiency (total N uptake/N applied) in year 3 was low (22.3%). Of the N taken up, ≈50% was removed at the end of the growing season in fruit and leaves. In fall of year 4, the trees contained about 20 g N of which 50% was partitioned into leaves and fruit, indicating that the annual N uptake by young dwarf apple trees is low (≈10 g/tree). Data were pooled to compare dry matter and N partitioning into two major sinks: fruit and shoot leaves. Total fruit dry weight increased, and in year 4, fruit size decreased with fruit number, indicating that growth was carbon (C) limited at high crop loads. The number of shoot leaves initiated in both years was unaffected by fruit number, but leaf size decreased as fruit number increased in year 4. In year 3, the amount of both remobilized and root-supplied N in fruit increased with fruit number, but the N content of the shoot leaf canopy was unaffected. In general, N and C partitioning were coupled and leaf N concentrations were high (2.8% to 3.2%), suggesting that the low uptake efficiency of fertilizer N resulted because the availability of N in the root zone greatly exceeded demand.
apical mineral gains. Mineral remobilization efficiencies were expressed as a percentage reduction in mineral content between day 0 and day 6. Results Flower abscission and opening. An average of 6.4 ± 0.6 mature flowers per raceme out
To study the distribution of foliar applied B in ‘Italian’ prune (Prunus domestica L.) trees, 500 ppm B solutions were applied in July, September, and October. Boron applied in September or October moved readily out of senescing leaves and apparently into adjacent flower buds and subtending tissues. Boron applied in mid summer (29 July) moved out of nonsenescing leaves at a similar rate. Flower buds accumulated B slowly in the fall and winter, but rapidly during bud swelling. In flowers, the largest increases in B concentrations due to foliar sprays were in anthers (248%) and styles (162%).
Whole shoots of Easter lily (Lilium longiflorum Thunb. cv. Nellie White) were exposed to 14CO2 at 25, 37, and 51 days after full bloom of the commercial crop. Seven days after each exposure, 20% of the total recovered 14C remained in the shoot, which included stem roots, 10-25% in stem bulblets, 11-20% in mother scales, and 34-44% in daughter scales. Sink activity increased sharply from the outer mother scales to the inner daughter scales. The fraction of total 14C in the main bulb decreased, while that in the stem bulblets increased at successive exposures. Another group of plants was labeled repeatedly by dosing with 14CO2 on the three previous occasions and, also, at 65 days after full bloom. Bulbs were harvested 7 days after the final exposure, stored at 18°C for 14 weeks, and then replanted, At bulb digging, 50%, 30%, and 20% of the total 14C recovered were in the main bulb, stem bulblets, and shoot, respectively. Mother scales lost dry weight and 14C during storage and were nearly depleted when flower buds were visible the next season. Specific 14C activity in the emerging flowering shoot was high but decreased dramatically as the leaf number rapidly increased. The shoot and new daughter scales were the principal recipients of mobilized scale reserves, although only 28% of the 14C lost from mother scales were recovered in other plant parts. A majority of the carbon originally in mother scales was likely lost in respiration between fall harvest and 3 weeks after anthesis the following year. The daughter bulb contained 64% of the 14C in the bulb at fall harvest, and lost very little 14C during regrowth the following year.
Grapevines (Vitis vinifera L.) were covered with an 80% neutral shade cloth from flowering until harvest to investigate effects of shade on early season vegetative development in the year after treatment. Shading reduced root dry weight, the concentration of soluble sugars, and amino nitrogen in xylem sap at budbreak, and leaf area expansion in the following year. Dry weight of roots on both shaded and nonshaded vines declined by more than 50% in the first 3 weeks after budbreak and then began to increase, but still had not recovered to prebudbreak levels, 10 weeks after budbreak. Total leaf area per shoot was reduced in the year after shading due to both fewer and smaller leaves.
The objective of this investigation was to determine the dynamics of carbohydrate use as revealed by soluble sugar and starch concentration in leaves, inflorescence buds, rachises, nuts, current and 1-year-old wood, and primary and tertiary scaffold branches and roots (≤10 mm in diameter) of alternate-bearing `Kerman' pistachio (Pistachia vera L.) trees that were in their natural bearing cycles. Two hypotheses were tested. First, carbohydrate concentration is greater early in the growing season in organs examined from heavily cropping (“on”) than light cropping (“off”) trees. This hypothesis was affirmed as judged by soluble sugar and starch concentration in leaves, inflorescence buds, rachises, nuts, current and 1-year-old wood, and primary and tertiary branches and roots of “on” compared to “off” trees. Second, carbohydrate concentration remains high in “on” tree organs as the first wave of inflorescence bud and nut abscission occurs early in the growing season. This hypothesis was also affirmed. In fact, soluble sugars and starch remained high in “on” trees through full bloom FB + 60 days (FB + 60) as inflorescence bud and nut abscission occurred. In the persisting “on” tree inflorescence buds, sharp decreases in soluble sugars and starch were evident by the final sample date when “off” tree inflorescence buds contained a 13 times greater concentration of soluble sugars and starch than “on” tree buds. At that time, “off” tree inflorescence buds contained 50% more dry mass than “on” tree inflorescence buds. After FB + 60, “on” tree soluble sugars and starch declined in all organs as nut growth occurred. During the same time period, organs of “off” trees began to accumulate greater concentrations of soluble sugars and starch and exceeded concentrations measured in organs of “on” trees.